Mg-al-ca-based master alloy for mg alloys, and a production method therefor

ABSTRACT

The present invention relates to an Mg—Al—Ca based master alloy for Mg alloys and to a production method therefor, and concerns an alloying master alloy used for magnesium or magnesium alloys. To this end, a feature of the invention is that, while the Ca:Al ration in the composition is maintained at between 7:3 and 1:9, based on percentages by weight in the alloy, a balance of Mg is added in an amount of up to 85% of the entire weight of the master alloy, based on percentage by weight. The production method comprises the steps of: preparing components of a master alloy by selecting a composition in which, while the Ca:Al ration in the composition is maintained at between 7:3 and 1:9, based on percentages by weight in the alloy, there is a balance of Mg in an amount of up to 85% of the entire weight of the master alloy, based on percentage by weight; sequentially melting Mg, Al and Ca; completely melting the components by applying an adequate amount of heat; and rapidly cooling the molten pool.

TECHNICAL FIELD

The present invention relates to an Mg—Al—Ca based master alloy for Mgalloys and a production method therefor.

BACKGROUND ART

Mg alloys have a density of approximately 1.8 g/cm³, which is a minimumof density levels of various alloys that are commercially available upto now, and demonstrate high specific strength and modulus ofelasticity. In particular, Mg alloys are excellent in view of absorbingcapability of vibrations or impacts, electrical and thermalconductivity, processibility, fatigue strength at high temperature,impact property, and so on. Specifically, Mg alloys have variousadvantageous properties complying with requirements for weight reductionin various fields including transportation equipment such asautomobiles, airplanes, or the like, equipment for defense industry,general machinery, and so on.

One of the most favorable advantages of Mg alloys is lightness inweight. Currently commercially available Mg alloys have a specificweight in a range of 1.79 to 1.81, which is approximately 35% or greaterlighter than Al alloys, and demonstrate excellent mechanical properties.That is to say, whereas Mg alloys are similar to Al or steel in view ofthe modulus of elasticity and density, they demonstrate a noticeablyreducing effect of weight, compared to Al alloys or plastic material.

Since the Mg alloy is melted at a relatively low temperature in a rangeof 650 to 680° C., although there is a slight difference in the meltingtemperature according to the kind of allying element used, a smallamount of energy is consumed in recycling the Mg alloy. In particular,the Mg alloy can be recycled only with a quarter of the energy requiredfor producing an Mg alloy ingot for the first time, therebydemonstrating a very high energy saving effect. The Mg alloy recoveredfrom the field production process may be melted to be recycled, followedby removing impurities and reducing components, and the recycled Mgalloy can be reused in substantially the same state as a new Mg alloy.In addition, Mg alloys are at least twice longer than Al alloys in viewof the life of molds, and are higher than Al alloys in view ofmanufacturability. Consequently, the production cost required by eachunitary part can be reduced.

If a group of elements are added at once in the manufacture of an alloy,they may not be properly mixed. Thus, in order to add alloying elementsto be used in uniform amounts, it is often the case that an alloycontaining large amounts of elements to be added is separately preparedas a flux, and small pieces of the flux are added to a molten metal usedas a parent material of a desired alloy to then be diluted. Here, thealloy containing large amounts of elements to be added is referred to asa master alloy. The master alloy is also called an intermediate alloy.

Al has the most advantageous effect when it is used as an alloyingelement of Mg. The addition of Al increases the strength and hardness ofMg alloys, improves flowability during casting and increases asolidifying range, thereby improving castability. When Al is added in anamount of 6 wt % or less, it may turn into solid-solution in an Mg base.On the other hand, when Al is added in an amount of greater than 6 wt %,it may be precipitated and cured by heat treatment. In general, in mostcommercially available alloys, the content of Al is 10 wt % or less, inwhich Al alloys have excellent physical properties in view of strengthand elongation. However, when Al reacts with Mg, an Mg₁₇Al₁₂ phase maybe formed, thereby lowering crepe resistance at high temperature.

Ca considerably improves high temperature strength and crepe resistanceof Mg—Al based Mg alloys. The addition of a trace amount (<0.5%) of Cato an Al containing Mg alloy forms an Al₂Ca intermetallic compound,which is stable at high temperature, during solidification, therebyincreasing the strength and heat resistance. In addition, it is alsoknown that Ca is an effective element in preventing alloys from beingoxidized during casting or heat treatment. Further, Ca may serve to makecrystalline particles into microstructures. However, Ca may reduceflowability of a molten metal, thereby deteriorating castability,facilitates hot tearing, and increasing viscosity with respect to a moldduring die casting, thereby ultimately lowering the manufacturability.If Ca is added in an amount of 0.3 wt % or greater, cracks may begenerated during welding.

When the conventional Ca alloying element is directly input into Mg orMg alloy for manufacturing Mg Alloy, solid-solution of Ca in the Mgalloy occurs in a certain amount, so that the conventional Ca alloyingelement turns into solid-solution in the Mg alloy base, rather thanforming a phase in the Mg ally base. In addition, when the conventionalCa alloying element is added to an Mg molten metal, which is highlybrittle, the yield with the addition of Ca is not high, but an oxidederived from Ca may be generated. For example, when Ca is added in anamount of 1.3 wt % or greater (0.8 wt % in a non-equilibrium state),dissolution of Ca in the Mg base is not further performed, and anintermetallic compound is formed. Typical examples of the intermetalliccompound affecting physical properties of Mg or other alloying elementsinclude Al₂Ca.

DISCLOSURE OF THE INVENTION Technical Problem

In order to overcome the above-mentioned shortcomings, the presentinvention provides a novel Mg—Al—Ca based master alloy for Mg alloys,which is different from alloying elements added for alloying to Mg or anMg alloy or a conventional master alloy, and a production methodtherefor. The Mg alloy produced using the master alloy according to thepresent invention demonstrates excellent physical properties, comparedto conventional Mg alloys. In the present invention, while a Ca:Alcomposition ratio is maintained at between 7:3 and 1:9, based onpercentages by weight in the alloy, a balance of Mg may be added in anamount of up to 85% of the entire weight of the master alloy, based onpercentage by weight.

The objects of the present invention are not limited to theabove-described objects and other objects not described above may beunderstood by those of ordinary skill in the art from the followingdescription of the preferred embodiments.

Technical Solution

According to an aspect of the invention, there is provided an Mg—Al—Cabased master alloy for Mg alloys, wherein while a Ca:Al compositionratio is maintained at between 7:3 and 1:9, based on percentages byweight in the alloy, a balance of Mg is added in an amount of up to 85%of the entire weight of the master alloy, based on percentage by weight.

Specifically, the Ca:Al composition ratio may be maintained at between6:4 and 2:8, based on percentages by weight.

The content of Al may be contained in an amount of 15% or greater of theentire weight of the Mg—Al—Ca based master alloy, based on percentage byweight.

While the Ca:Al composition ratio is maintained at 4.3:5.7, Mg may becontained in an amount of 65% of the entire weight of the master alloy,based on percentage by weight.

According to an aspect of the invention, there is provided a productionmethod of an Mg—Al—Ca based master alloy for Mg alloys, the productionmethod including preparing components of a master alloy by selecting acomposition in which, while a Ca:Al composition ratio is maintained atbetween 7:3 and 1:9, based on percentages by weight in the alloy, thereis a balance of Mg in an amount of up to 85% of the entire weight of themaster alloy, based on percentage by weight, sequentially melting Mg, Aland Ca, completely melting the components by applying an adequate amountof heat, and solidifying the molten metal.

The solidifying of the molten metal may include rapidly cooling themolten metal.

The Ca:Al composition ratio may be maintained at between 6:4 and 2:8,based on percentages by weight.

The content of Al may be contained in an amount of 15% or greater of theentire weight of the Mg—Al—Ca based master alloy, based on percentage byweight.

In the melting, Mg may first be melted, Al may then be melted, and Camay finally be melted.

In the melting, Al may first be melted, Mg may then be melted, and Camay finally be melted.

In the melting, Mg and Al may be melted together and Ca may then bemelted.

In the melting, Mg and Ca may be melted together and Al may then bemelted.

Advantageous Effects

As described above, the master alloy according to the present inventionis used in producing Mg alloys having excellent physical properties bycontrolling components of alloying elements added to producecommercially available Mg alloys within composition ranges to causeAl₂Ca phase formation. That is to say, the Al₂Ca phase formed from themaster alloy is maintained in the final Mg alloy, thereby making the Mgalloy have a microstructure and increasing yield strength and thetensile strength of the Mg alloy. In addition, formation of a β-Mg₁₇Al₁₂phase that is thermally unstable is suppressed, and casting defects canbe greatly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a calculated phase diagram of Al—Ca binary alloys;

FIG. 2 is a calculated phase diagram of Mg—Al binary alloys;

FIG. 3 is a calculated phase diagram of Mg—Ca binary alloys;

FIG. 4 is a graph illustrating composition ranges (region 1) accordingto an embodiment of the present invention on a liquid projection view ofan Mg—Al—Ca ternary phase diagram indicated by weight ratios; and

FIG. 5 is a graph illustrating composition ranges (region 2) accordingto another embodiment of the present invention on a liquid projectionview of an Mg—Al—Ca ternary phase diagram indicated by weight ratios.

MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. In everypossible case, like reference numerals are used for referring to thesame or similar elements in the description and drawings. Moreover,detailed descriptions related to well-known functions or configurationswill be ruled out in order not to unnecessarily obscure subject mattersof the present invention.

The present invention provides an Mg—Al—Ca based master alloy, which isdifferent from the conventional alloying element or conventional masteralloy added to Mg or an Mg alloy for alloying, and a production methodtherefor, in an attempt to develop Mg alloys having better physicalproperties than conventional Mg alloy using the master alloy accordingto the present invention.

When the conventional Ca alloying element is directly input into Mg orMg alloy for manufacturing Mg Alloy, solid-solution of Ca in the Mgalloy occurs in a certain amount, so that the conventional Ca alloyingelement turns into solid-solution in the Mg alloy base, rather thanforming a phase in the Mg ally base. In addition, when the conventionalCa alloying element is added to an Mg molten metal, which is highlybrittle, the yield with the addition of Ca is not high, but an oxidederived from Ca may be generated. For example, when Ca is added in anamount of 1.3 wt % or greater (0.8 wt % in a non-equilibrium state),dissolution of Ca in the Mg base is not further performed, and anintermetallic compound is formed. Typical examples of the intermetalliccompound affecting physical properties of Mg or other alloying elementsinclude Al₂Ca.

In the present invention, the inputting of the alloying element usingthe master alloy is achieved by inputting comprises inputting anMg—Al—Ca master alloy prepared to cause Al₂Ca phase formation to Mg oran Mg alloy. As the result, the obtained Mg alloy has better physicalproperties than the conventional Mg alloy obtained by adding alloyingelements of the same composition. Here, in order to obtain a desiredcomposition, Ca or Al may further be added in addition to the masteralloy.

FIG. 1 is a calculated phase diagram of Al—Ca binary alloy. It can beconfirmed that intermetallic compounds are formed in various compositionranges. Examples of the intermetallic compound may include Al₄Ca, Al₂Ca,Al₁₄Ca₁₃ and Al₃Ca₈. Specifically, Al₂Ca has a considerably high meltingpoint. It is understood that Al₂Ca, observed in the present inventionfor the purpose of improving physical properties, is an intermetalliccompound having a high melting point. A method of calculating andobtaining a phase diagram is generally known in the related art. Inparticular, a commercially available program, such as a CALPHAD method,may also be used in calculating and obtaining the phase diagram.

FIG. 2 is a calculated phase diagram of Mg—Al binary alloys. As shown inFIG. 2, there is high solid solubility of either Mg or Al with respectto each opponent element. While Mg and Al are mixed together and melted,melting points thereof are lowered.

FIG. 3 is a calculated phase diagram of Mg—Ca binary alloys. Mg₂Caexists as an intermetallic compound between the Mg—Ca binary alloys. Themelting point of Mg₂Ca is positioned between melting points between pureMg and pure Ca. That is to say, the melting point of Mg₂Ca is higherthan the melting point of pure Mg and lower than the melting point ofpure Ca.

FIGS. 4 and 5 are liquid projection views of Mg—Al—Ca ternary phasediagrams indicated by weight ratios. Composition ranges of the masteralloy developed according to the present invention and exemplaryembodiments thereof are illustrated in FIGS. 4 and 5. In the ternaryphase diagram, vertexes of a triangle indicates points at whichfractions of components Mg, Ca and Al are 100%, respectively, and sidesof the triangle indicate binary system of two components on each of thesides.

As shown in FIGS. 4 and 5, as the temperature is lowered, Al2Ca ispresent in the wider composition range. By contrast, as temperature islowered, Al₄Ca, Al₁₄Ca₁₃, Mg₂Ca and Al₃Ca₈ are present in narrowercomposition ranges. In all of the figures (FIGS. 1 to 5), thetemperatures can be calculated in terms of degrees in Celsius (C) bysimply subtracting 273 from temperature values indicated in terms ofdegrees in Kelvin (K).

The Mg—Al—Ca based master alloy for Mg alloys produced in the presentinvention maintains a Ca:Al composition ratio at between 7:3 and 1:9,based on percentages by weight. As shown in FIG. 4, the line of theCa:Al composition ratio being 7:3 is maintained along the line {circlearound (1)}, and the line of the Ca:Al composition ratio being 1:9 ismaintained along the line {circle around (2)}. In the present invention,what is meant by the expression “the Ca:Al composition ratio ismaintained at between 7:3 and 1:9, based on percentages by weight” isthat the ranges of components of the master alloy are established belowthe line 1 and above the line {circle around (2)}.

In addition, according to the present invent, while the Ca:Alcomposition ratio is maintained at between 7:3 and 1:9, based onpercentages by weight, Mg is further added in an amount of up to 85% ofthe entire weight of the master alloy, based on percentage by weight,which is established above line {circle around (3)}.

In the present invention, the compositions for the master alloy aredetermined in a region established by the lines {circle around (1)},{circle around (2)} and {circle around (3)}, indicated by a region 1.That is to say, the master alloy is produced within the compositionrange of the region 1 established by the lines {circle around (1)},{circle around (2)} and {circle around (3)}.

More preferably, the Ca:Al composition ratio is maintained at between6:4 and 2:8, which are composition ranges formed by lines {circle around(4)}, {circle around (5)} and {circle around (3)}, as shown in FIG. 5.That is to say, in the case where the Ca:Al composition ratio ismaintained at between 6:4 and 2:8, the compositions for the master alloyare determined in a region established by the lines {circle around (4)},{circle around (5)} and {circle around (3)}.

In the Ca:Al composition ratio, 6:4 is more preferred than 7:3 for thereason below. That is to say, when the composition range is shiftedtoward Al₂Ca from the region established by Mg₂Ca, Al₁₄Ca₁₃ and Al₂Ca,Al₂Ca formation is more securely guaranteed. That is to say, since the7:3 composition ratios exists around boundary lines between Mg₂Ca,Al₁₄Ca₁₃ and Al₂Ca, there are also possibilities of forming Mg₂Ca andAl₁₄Ca₁₃, rather than Al₂Ca. However, the 6:4 composition ratios canmake Al2Ca formation more securely confirmed.

In the Ca:Al composition ratio, 2:8 is more preferred than 1:9 for thereason below. That is to say, when the composition range is shiftedtoward Al₂Ca from the region established by Al₂Ca and Al₄Ca, Al₂Caformation is more securely guaranteed. That is to say, since the 1:9composition ratios exists around a boundary line between Al₂Ca andAl₄Ca, there is also possibility of forming Al₄Ca, rather than Al₂Ca.However, the 2:8 composition ratios can make Al2Ca formation moresecurely confirmed.

In addition, a feature of the present invention lies in that the contentof Al is contained in an amount of 15% or greater of the entire weightof the Mg—Al—Ca based master alloy, based on percentage by weight. Ifthe content of Al is less than 15%, an amount of Al2Ca formed isreduced. In this case, the effect of Al₂Ca as a master alloy may becomeinsignificant.

A production method of an Mg—Al—Ca based master alloy for Mg alloysaccording to an embodiment of the present invention includes preparingcomponents of a master alloy by selecting a composition in which, whilea Ca:Al composition ratio is maintained at between 7:3 and 1:9, based onpercentages by weight in the alloy, there is a balance of Mg in anamount of up to 85% of the entire weight of the master alloy, based onpercentage by weight, sequentially melting Mg, Al and Ca, completelymelting the components by applying an adequate amount of heat, andsolidifying the molten metal. Preferably, in the solidifying of themolten metal, the molten metal may be rapidly cooled. Here, the rapidlycooling refers to forced cooling, which is faster than naturalsolidifying in a general casting process. The forced cooling includeswater cooling (including brine quenching) or rapid cooling by blowingair quenching.

Here, the composition selected for producing the Mg—Al—Ca based masteralloy is determined in the range of the region 1 shown in FIG. 4. Thereason of the foregoing is briefly described. That is to say, the alloycomponents are completely melted by raising the temperature over theliquid phase line of the corresponding composition of the region 1, andthe molten metal is then rapidly cooled, thereby maximally producingAl₂Ca as desired in the master alloy of the present invention.

More preferably, the Ca:Al composition ratio may be maintained atbetween 6:4 and 2:8, based on percentage by weight. The compositionselected for producing the Mg—Al—Ca based master alloy is determined inthe range of the region 2 shown in FIG. 5, established by the lines{circle around (4)}, {circle around (5)} and {circle around (3)}. Asdescribed above, in the Ca:Al composition ratio, 6:4 is more preferredthan 7:3 because when the composition range is shifted toward Al₂Ca fromthe region established by Mg₂Ca, Al₁₄Ca₁₃ and Al₂Ca, Al₂Ca formation ismore securely guaranteed. That is to say, since the 7:3 compositionratios exists around boundary lines between Mg₂Ca, Al₁₄Ca₁₃ and Al₂Ca,there are also possibilities of forming Mg₂Ca and Al₁₄Ca₁₃, rather thanAl₂Ca. However, the 6:4 composition ratios can make Al₂Ca formation moresecurely confirmed.

In the Ca:Al composition ratio, 2:8 is more preferred than 1:9 for thereason below. That is to say, when the composition range is shiftedtoward Al2Ca from the region established by Al₂Ca and Al₄Ca, Al₂Caformation is more securely guaranteed. That is to say, since the 1:9composition ratios exists around a boundary line between Al₂Ca andAl₄Ca, there is also possibility of forming Al₄Ca, rather than Al₂Ca.However, the 2:8 composition ratios can make Al₂Ca formation moresecurely confirmed. More preferably, while the Ca:Al composition ratiois maintained at 4.3:5.7, Mg is contained in an amount of 65% of theentire weight of the master alloy, based on percentage by weight. Whenthe Ca:Al composition ratio is 4.3:5.7 by wt %, maximum Al₂Ca phaseformation can be expected by maintaining a molar ratio of Ca:Al at 1:2.As confirmed from FIG. 5 (Al₂Ca line), when Mg is contained in an amountof 65% or less, Al₂Ca phase formation can be more securely guaranteed.

As shown in FIG. 5, on the Al2Ca line, Al and Ca maintain the Al₂Cacomposition ratio. An ideal amount of Al₂Ca can be formed by adding Mgwhile maintaining the composition ratio on the Al₂Ca line. In this case,Mg is more preferably added in an amount of up to 65% of the entireweight of the master alloy, based on percentage by weight.

Melting Methods of Various Components

Various components for forming the Mg—Al—Ca based master alloy accordingto the present invention are prepared, and Mg, Al and Ca aresequentially melted one by one. For example, Mg is melted by applying anadequate amount of heat, Al is then melted, and Ca is finally melted.

Here, the melting may also be performed from Mg to Al and to Ca, Al toCa and to Mg, or Ca to Mg and to Al in that order. As shown in FIGS. 1,2 and 3, when an intermetallic compound is generated during melting, themolten metal can only be formed by applying a much larger amount of heatdue to a high melting point of the generated intermetallic compound,which is disadvantageous. Therefore, when the respective components aremelted, it is not desirable to form Al₂Ca from the beginning by meltingAl and Ca together. Therefore, the melting in the order of Al—Ca—Mg orCa—Al—Mg is the most undesirable method.

Unlike the melting order stated above, Mg and Al may be melted together,or Ca and Mg may be melted together, and the rest alloying element (Caor Al) may then be melted. As described above, in order to prevent theAl2Ca intermetallic compound from being immediately formed beforeforming the master alloy, it is least desirable to melt Al and Ca at thesame time. As confirmed from FIGS. 1, 2 and 3, with regard to cases ofAl and Mg, and Ca and Mg, except for a case of Al and Ca, when twometals are melted at the same time, the melting point is lowered,compared to a case when a pure metal is melted. Of course, with regardto a case of a Ca—Mg binary system, when two metals are melted at thesame time, compared to the case when pure Ca or Mg is melted, themelting point decreased in a certain composition range and increasedafter passing an eutectic point. However, it can also be confirmed thata temperature at which the intermetallic compound of Mg2Ca is formed islower than the melting temperature of Ca.

Here, three components Mg, Al and Ca may also be melted at the sametime. When the three components Mg, Al and Ca are put into a crucibleand an adequate amount of heat for melting is applied in a protectiongas atmosphere, they are melted in the crucible, thereby forming amolten metal for forming the Mg—Al—Ca based master alloy. In a casewhere ignition occurs due to the Mg or Ca composition, melting may beperformed in the protection gas atmosphere.

Melting Temperature in Producing Master Alloy

In the present invention, the melting temperature for forming the moltenmetal is as high as a temperature in which a solid phase metal issufficiently melted to then exist a perfect liquid phase. However,considering that the temperature of the molten metal may be lowered withaddition of sequentially input components, it is necessary to maintainthe molten metal to be in a temperature range having a sufficientmargin. In metallography, it is generally often the case that themelting point is lowered according to the progress of alloying.

If the melting temperature is excessively raised, evaporation of aliquid metal may occur, and Mg or Ca may be readily evaporated in viewof its characteristic, resulting in a loss of the amount of the moltenmetal, thereby adversely affecting final physical properties due toignited oxides.

In order to form the molten metal of the master alloy, the molten metalis preferably stirred. The stifling may be performed by generating anelectric field by providing an apparatus for applying an electromagneticfield around a furnace containing the molten metal, thereby inducingconvection of the molten metal. Alternatively, the molten metal may bemechanically stirred from the outside.

In Table 1 below, after producing the master alloy with the compositionsin the composition ranges of the region 1 or 2, Al₂Ca formation in themaster alloy was confirmed. In order to allow Al₂Ca in a liquid phase toexist in a solid phase, casting is preferably performed on the moltenmetal by rapid cooling. The rapid cooling is performed because it cannotbe confirmed into which phase the liquid phase Al₂Ca is converted as theresult of cooling. That is to say, the rapid cooling is performed forthe purpose of maintaining Al₂Ca in the liquid phase at high temperatureto be present as much as possible even in a solid phase at roomtemperature. FIG. 4 shows compositions a to j listed in Table 1 below.

TABLE 1 Composition Mg wt % Al wt % Ca wt % Al₂Ca formation a 10 30 60Confirmed b 10 50 40 Confirmed c 20 45 35 Confirmed d 30 35 35 Confirmede 30 60 10 Confirmed f 40 24 36 Confirmed g 40 40 20 Confirmed h 50 1832 Confirmed i 60 18 22 Confirmed j 70 20 10 Confirmed

The components of the respective alloys shown in Table 1 were melted atsufficiently high temperatures according to the melting method of thepresent invention. In Table 1, the presence of Al₂Ca was confirmed byX-ray diffraction. Here, the content of Al₂Ca was not measured.

Table 2 shows yield strengths of final Mg alloys obtained by inputtingthe master alloy produced by the present invention to Mg or Mg alloysaccording to composition ratios. Table 3 shows measuring results ofyield strengths of Mg alloys of Comparative Examples having the samecomposition ratios with those of Examples of the present invention bydirectly adding Al and/or Ca to the final Mg alloys, instead of addingthe master alloy produced by the present invention. Numbers foridentifying the respective examples shown in Table 2 correspond to thosefor identifying the respective comparative examples shown in Table 3.When Mg alloys are produced using the master alloy with Al₂Ca formed inthe present invention, they exhibited higher yield strengths thangeneral Mg alloys having the same composition ratios.

The reason of the foregoing is presumably caused by a large amount ofAl₂Ca as the intermetallic compound contained in the master alloyfinally produced by the present invention. Accordingly, physicalproperties of the Mg alloys are improved.

In addition, it was confirmed that the Mg alloy was microstructured withthe addition of the master alloy produced by the present invention.Further, it was confirmed that Mg₂Ca or (Mg, Al)₂Ca phases in additionto Al₂Ca were distributed in the Mg alloy base.

TABLE 2 Example Composition Ratio (wt %) Yield Strength [MPa] 1Mg—4Al—0.5Ca 127 2 Mg—5Al—0.5Ca 139 3 Mg—6Al—0.5Ca 151 4 Mg—4Al—1.0Ca135 5 Mg—5Al—1.0Ca 149 6 Mg—6Al—1.0Ca 158

It is noted that the composition ratios listed in Tables 2 and 3indicate compositions of the final Mg alloys produced using the masteralloy according to the present invention.

TABLE 3 Comparative Yield Strength Example Composition Ratio (wt %)[MPa] 1 Mg—4Al—0.5Ca 109 2 Mg—5Al—0.5Ca 115 3 Mg—6Al—0.5Ca 126 4Mg—4Al—1.0Ca 112 5 Mg—5Al—1.0Ca 128 6 Mg—6Al—1.0Ca 135

Table 4 below shows comparison results of Ca yields when Mg-5Al-2Ca isproduced by adding 10Mg-50Al-40Ca as the inventive master alloy to Mg,by wt %, and directly adding Ca as an alloying element to Mg or an Mgalloy. Additionally, when necessary, Al is further added to adjust thefinal composition to Mg-5Al-2Ca. Here, the yield means a percentileobtained by dividing the amount of finally alloyed Ca in the Mg alloy bya total input amount of Ca.

As confirmed from Table 4 below, when Ca was added as an alloyingelement through the master alloy, the recovery rate of Ca was higherthan that in a case when Ca is directly added as the alloying element.The reason of the forgoing is that alloying may not be performed wellwhen Ca is directly added.

TABLE 4 Yield with Composition Ratio (wt %) addition of Ca ExampleAddition of 10Mg—50Al—40Ca master 95% alloy Comparative Direct additionof Ca 72% Example

As described above, it can be confirmed that the Mg alloy ismicrostructured with the addition of the master alloy produced by thepresent invention with the addition of the master alloy and Mg2Ca, Al2Caor (Mg, Al)₂Ca phases are uniformly distributed in the Mg alloy. Inaddition, In addition, formation of a β-Mg17Al12 phase that is thermallyunstable can be suppressed, and casting defects can be greatly reduced.As the result, the yield strengths of the Mg alloys were increased andthe tensile strengths of the Mg alloys were also increased.

The Mg—Al—Ca based master alloy produced according to the presentinvention may be added as an alloying means to one selected from thegroup consisting of pure Mg, Mg alloys and equivalents thereof. Inaddition, usable examples of the Mg alloy may include AZ91D, AM20, AM30,AM50, AM60, AZ31, AS41, AS31, AS21X, AE42, AE44, AX51, AX52, AJ50X,AJ52X, AJ62X, MRI153, MRI230, AM-HP2, Mg—Al, Mg—Al—Re, Mg—Al—Sn,Mg—Zn—Sn, Mg—Si, and Mg—Zn—Y, but aspects of the present invention arenot limited thereto. Any Mg alloy that is generally used in industriesmay be used.

Although exemplary embodiments of the present invention have beendescribed in detail hereinabove, it should be understood that manyvariations and modifications of the basic inventive concept hereindescribed, which may appear to those skilled in the art, will still fallwithin the spirit and scope of the exemplary embodiments of the presentinvention as defined by the appended claims.

1. An Mg—Al—Ca based master alloy for Mg alloys, wherein while a Ca:Alcomposition ratio is maintained at between 7:3 and 1:9, based onpercentages by weight in the alloy, a balance of Mg is added in anamount of up to 85% of the entire weight of the master alloy, based onpercentage by weight.
 2. The Mg—Al—Ca based master alloy of claim 1,wherein the Ca:Al composition ratio is maintained at between 6:4 and2:8, based on percentages by weight.
 3. The Mg—Al—Ca based master alloyof claim 1, wherein the content of Al is contained in an amount of 15%or greater of the entire weight of the Mg—Al—Ca based master alloy,based on percentage by weight.
 4. The Mg—Al—Ca based master alloy ofclaim 1, wherein while the Ca:Al composition ratio is maintained at4.3:5.7, Mg is contained in an amount of 65% of the entire weight of themaster alloy, based on percentage by weight.
 5. A production method ofan Mg—Al—Ca based master alloy for Mg alloys, the production methodcomprising: preparing components of a master alloy by selecting acomposition in which, while a Ca:Al composition ratio is maintained atbetween 7:3 and 1:9, based on percentages by weight in the alloy, thereis a balance of Mg in an amount of up to 85% of the entire weight of themaster alloy, based on percentage by weight; sequentially melting Mg, Aland Ca; completely melting the components by applying an adequate amountof heat; and solidifying the molten metal.
 6. The production method ofclaim 5, wherein the solidifying of the molten metal comprises rapidlycooling the molten metal.
 7. The production method of claim 5, whereinthe Ca:Al composition ratio is maintained at between 6:4 and 2:8, basedon percentages by weight.
 8. The production method of claim 5, whereinthe content of Al is contained in an amount of 15% or greater of theentire weight of the Mg—Al—Ca based master alloy, based on percentage byweight.
 9. The production method of claim 5, wherein in the melting, Mgis first melted, Al is then melted, and Ca is finally melted.
 10. Theproduction method of claim 5, wherein in the melting, Al is firstmelted, Mg is then melted, and Ca is finally melted.
 11. The productionmethod of claim 5, wherein in the melting, Mg and Al are melted togetherand Ca is then melted.
 12. The production method of claim 5, wherein inthe melting, Mg and Ca are melted together and Al is then melted. 13.The Mg—Al—Ca based master alloy of claim 2, wherein the content of Al iscontained in an amount of 15% or greater of the entire weight of theMg—Al—Ca based master alloy, based on percentage by weight.
 14. TheMg—Al—Ca based master alloy of claim 2, wherein while the Ca:Alcomposition ratio is maintained at 4.3:5.7, Mg is contained in an amountof 65% of the entire weight of the master alloy, based on percentage byweight.
 15. The production method of claim 6, wherein the Ca:Alcomposition ratio is maintained at between 6:4 and 2:8, based onpercentages by weight.
 16. The production method of claim 6, wherein thecontent of Al is contained in an amount of 15% or greater of the entireweight of the Mg—Al—Ca based master alloy, based on percentage byweight.
 17. The production method of claim 6, wherein in the melting, Mgis first melted, Al is then melted, and Ca is finally melted.
 18. Theproduction method of claim 6, wherein in the melting, Al is firstmelted, Mg is then melted, and Ca is finally melted.
 19. The productionmethod of claim 6, wherein in the melting, Mg and Al are melted togetherand Ca is then melted.
 20. The production method of claim 6, wherein inthe melting, Mg and Ca are melted together and Al is then melted.